Many types of storage devices have emerged throughout the years with different characteristics. To keep up with today's CPU frequencies, one needs a fast memory device, able to serve requests within a few clock cycles. Nearly all commercial database systems rely on caching techniques to improve performance. Caches are often implemented in memory that can be accessed quickly, such as random access memory (RAM) and static random access memory (SRAM), as opposed to storage that takes longer to access, such as disk-based storage. Caches typically store frequently used data and reduce the time needed by a database system to access a data page. RAM, however, is much more costly than disk-based storage.
In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.